题型:阅读理解 题类:常考题 难易度:普通
江西省赣州市2017-2018学年高一下学期英语期末考试试卷
Think of a seed buried in a pot. It's dark down there in the potting soil. There's no light, no sunshine. So how does it know which way is up and which way is down? It does know. Seeds send shoots up toward the sky, and roots the other way. Darkness doesn't confuse them. Somehow, they get it right.
More surprisingly, if you turn a seedling (秧苗) or a whole bunch of seedlings upside down, as Thomas Andrew Knight of the Royal Society did around 200 years ago, the tips and roots of the plant will sense, “Hey, I'm upside down. Look! I. will turn my way to the right direction and do a U-turn.”
How do they know? According to botanist Daniel Chamovitz, Thomas Knight about 200 years ago guessed that plants must sense gravity. Knight proved it with a crazy experiment involving a spinning plate.
He attached a bunch of plant seedlings onto a disc. The plate was then turned by a water wheel powered by a local stream at a speed of 150 revolutions (旋转) per minute for several days.
If you have been at an amusement park in a spinning teacup, you know that because of centrifugal force (离心力) you get pushed away from the center of the spinning object toward the outside.
Knight wondered, would the plants respond to the centrifugal pull of gravity and point their roots to the outside of the spinning plate? When he looked, that's what they'd done. Every plant on the disc had responded to the pull of gravity, and pointed its roots to the outside. The roots pointed out, and the shoots pointed in. So Thomas Knight proved that plants can and do sense the pull.
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